Abstract:

Power systems are required to achieve a balance between generation and consumption in order to function. This task has conventionally been performed mainly by generators following the electricity demand. However, such a paradigm is changing along with the emerging of variable power generation. While a part of the generation becomes more variable, the rest of the power plants are left with increased responsibility to maintain the power balance. To assist with the balance maintenance, the electricity consumption can also be employed to provide the power system with flexibility. This demand-side flexibility, or demand response (DR), is the focus in this thesis.

The aim of the dissertation is to propose a framework for the harnessing of DR for power system flexibility with a particular focus on residential heating loads. The topic is divided into three objectives, which are covered in this thesis and the publications. Firstly, the dissertation focuses on load aggregation whose purpose is to make the distributed and small flexibility resources visible and controllable. A central part of the aggregation approach is an aggregator, an entity acting as an intermediary between the loads and power system markets. The aggregator's daily operation is assisted by a virtual power plant, which automatically operates and responds to different situations in the maintenance of power system balance.

Secondly, the thesis proposes three coordination strategies for the scheduling and control of DR. The strategies focus on different markets and parts of the power balance maintenance process, including a day-ahead electricity market, a balancing power market, and the manipulation of consumption patterns. At the same time, they provide alternative approaches for the interaction between the aggregator and consumers. The first of the introduced strategies emphasizes local decision-making and control, the second centralized, and the third is a combination of local and centralized. The functionality of the proposed strategies is tested with simulation studies.

Thirdly, the thesis considers the utilization of DR in the power system frequency control. This application enables the loads to contribute to the power balance in the cases of disturbances and other unforeseen imbalances. Within the proposed framework, thermostatically controlled loads are able to react to the system frequency locally and to provide frequency containment reserves (FCR). Furthermore, the aggregator can centrally control loads in order to assists in frequency restoration. It is also argued with simulations that with a proper frequency coordination, the potential of DR to provide FCR can be improved.Voimajärjestelmissä kulutuksen ja tuotannon täytyy olla joka hetki tasapainossa, mikä on perinteisesti saavutettu sähkönkulutusta seuraavilla voimalaitoksilla. Tasapainon saavuttaminen tulee kuitenkin haastavammaksi vaihtelevan sähköntuotannon määrän lisääntyessä, kun perinteisiä voimaloita poistuu järjestelmästä ja sen tarvitsema jousto kasvaa. Kasvavaa jouston tarvetta voidaan helpottaa ohjaamalla sähkönkulutusta vastaamaan voimajärjestelmän tarpeita. Joustava ja ohjattava sähkönkulutus eli kysyntäjousto on myös tämän työn aiheena.